Exception in documentation example of `toDataFrame`

In [Operations/Create/DataFrame](https://kotlin.github.io/dataframe/createdataframe.html#todataframe) we have:

```kt
val df = students.toDataFrame {
// add column
"year of birth" from { 2021 - it.age }

// scan all properties
properties(maxDepth = 1) {
exclude(Score::subject) // `subject` property will be skipped from object graph traversal
preserve() // `Name` objects will be stored as-is without transformation into DataFrame
}

// add column group
"summary" {
"max score" from { it.scores.maxOf { it.value } }
"min score" from { it.scores.minOf { it.value } }
}
}
```
Executing this in a Kotlin Notebook cell results in: `Exception while analyzing expression in (13,28) in Line_123.jupyter.kts`

Line 13 refers to `"max score" from { it.scores.maxOf { it.value } }`

Gradle settings:

```kts
plugins {
kotlin("jvm") version "2.2.20-Beta1"
kotlin("plugin.dataframe") version "2.2.20-Beta1"
}

dependencies {
implementation("org.jetbrains.kotlinx:dataframe:1.0.0-Beta2")
testImplementation(kotlin("test"))
}

```

Start with the `Operations/Create/DataFrame` documentation example at the linked `toDataFrame` section, using the supplied Kotlin and DataFrame Gradle versions in a Kotlin Notebook. Reproduce the exception on the `"max score" from` line and determine the documentation change needed so the example executes without that error.

Written by the indexing model from the issue text.